Tutoring English, vocabulary is always of interest. The tutor brings up the words occlude and occlusion.

Occlude means to obstruct, so an occlusion is an obstruction. You might argue, for instance, that during an eclipse, the moon occludes light from reaching Earth. The moon, in that case, is an occlusion.

Merriam-Webster, however, expands on the definition of occlude, suggesting it also means to unite, as would two surfaces brought together (the example given is sets of teeth). From that point of view, the door edge and the door seal occlude, forming an occlusion that keeps water from leaking in.

Source:

Merriam-Webster Dictionary. Springfield: Merriam-Webster, 2004.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.